1. Field of the Invention
This invention relates to actuators for use in connection with medicinal aerosol formulations.
2. Description of the Related Art
Pulmonary disorders such as asthma, chronic bronchitis, emphysema, and chronic obstructive pulmonary disease are often treated with drugs contained in medicinal aerosol formulations. Such formulations are commonly delivered using a metered dose inhaler ("MDI") that is designed to expel a dose of the drug in a form that can be inhaled into the lung, where the drug can exert its desired local therapeutic effect. With MDIs involving propellant based formulations the dose is expelled at a high velocity and in the form of particles or droplets from which the propellant preferably evaporates prior to inhalation. With many such MDIs a significant fraction of the expelled dose does not reach the lung; rather it is deposited in the mouth, the throat, or the upper airways where it is not therapeutically effective.
The turbulent nature of the fluid flow in an aerosol actuator when taken together with the presence of particles (and the variable size of such particles) in the aerosol dose makes difficult the design of improved actuators. Devices have been designed to increase the fraction of the expelled dose that can reach the lungs. Spacers, which allow the expelled dose to decelerate and allow time for evaporation of propellant, have been used to some advantage. These devices, however, are rather large and relatively inconvenient. U.S. Pat. No. 5,115,803 (Sioutas) describes a device that uses the energy of the expelled dose to create shear forces that break up particle agglomerates, thereby increasing the fraction of the drug that is present in the form of particles of respirable size. This device also decelerates the particles such that they are present in the form of a cloud that can be inhaled. Other problems have been addressed through actuator design. For example, U.S. Pat. No. 5,048,729 (Pritchard) describes an aerosol dispenser involving an applicator that includes a frustoconical diverter with a small orifice of diameter 0.5 mm facing a valve orifice. Aerosol droplets are said to predominantly pass through the orifice, decelerate, and be inhaled, while the propellant gas is predominantly diverted out of the dispenser.